JP2002530898A - L-band amplification using detuned 980 nm excitation light - Google Patents

Abstract

  (57) [Summary] A method for driving an optical amplifier having improved gain and pumping light-signal light conversion efficiency in a long wavelength region (L band) of an emission spectrum of a rare earth-doped gain medium having a known excitation absorption band, comprising a large signal input. Driving an optical amplifier, comprising: providing an optical signal having an intensity to the amplifier; and supplying the amplifier with pump light having a wavelength different from the known center wavelength of the excitation absorption band for the optical signal to be amplified. Method. Signal gain and improved pump-to-signal conversion efficiency have been demonstrated for erbium L-band signals with pump light detuned within ± 0-30 nm above and below the pump band center wavelength 979-980 nm. A method for driving an optical amplifier is also disclosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Industrial applications]

The present invention relates to an optical amplifier, and more particularly to a method for improving L-band amplification using detuned 980 nm pump light, and an apparatus using the method.

[0002]

[Prior art]

Optical communication service providers are continually demanding higher data capabilities and higher data rates as the services customers need today and in the future. Optical amplifiers used in the system, especially erbium-doped fiber amplifiers (
The channel density of an EDFA is limited by the available gain wavelength bandwidth of an erbium-doped fiber amplifier (EDFA). Even when a gain flat filter is applied to a flattened erbium gain spectrum for multi-channel amplification, this wavelength width is about 35 nm. Three technologies to increase the system capacity of a multi-channel system using optical fiber are: (1) increasing the bit rate per channel, (2) increasing the number of channels by narrowing the channel spacing, and (3) gain medium. Increasing the total gain / transfer bandwidth inside to increase the number of channels. Increasing the number of bits per channel is not always a viable solution because many existing systems cannot operate above the current OC-48 bit rate (2.5 Gb / s). Similarly, the non-linearity of the fiber limits the narrowing of the channel spacing below the current 50-100 GHz. For this reason, the method of increasing the gain bandwidth of an erbium-doped fiber amplifier (EDFA) has been recognized as a direct measure to increase system performance while maintaining channel spacing and bit rate per channel. In 1990, Ainsul (Ai
nslie) et al. studied the effectiveness of erbium gain wavelengths in the long wavelength band (1565-1610 nm). This is the subject of Electronics Letters,
Vol. 26, pp. 1645-1646 (1990) "1.6μ wide area band with a high gain Er ³⁺ doped silica fiber amplifier" (High gain, broadband 1.6 micron Er 3+ doped silica fiber
amplifier, Electronics Letters, volume 26, pp. 1645-1646 (1990)). Recently, Srivastava et al., 1.6 micron band (
In the L band), the application of erbium-doped fiber amplifier (EDFA) quartz fiber has been demonstrated. This is the technology digest OFC 1998,
Post-deadline paper PD10-1, San Jose, California, 1998, "1 Tb / s transmission of 100 WDM 10 Gb over 400 km over 100 km using 100 WDM channels per channel over real wavelength fiber" / s chann
els over 400km of Truewave fiber, Tech.Dig OFC'98, Post deadline paper
PD 10-1, San Jose, California, 1998). Sun and others,
The separation band structure of the amplifier for both the general C band (1530-1560 nm) and the L band was discussed, resulting in a total gain bandwidth of 80 nm. This is the same as PROC. OAA
, Post Deadline newspaper PD2-2, Victoria, British Columbia,
"Ultrawide band erbium-doped silica fiber amplifier with 80 nm bandwidth", Canada (1997)
ifier with 80nm of bandwidth, PROC.OAA, Post deadline paper PD2-2, Vict
oria, BC Canada (1997)). As described above, L-band amplification is an undeveloped, but in a wavelength division multiplexer (WDM) system using optical fibers,
It offers a clear solution to bandwidth limitations.

[0003] The following is known by those skilled in the art. That is, in the L band region (here, about
Erbium-doped fiber amplifiers (EDFAs) operating in the spectral region of 1560 to about 1615 nm are typically designed to operate in the very popular C-band, in the region of about 1530 to about 1560 nm. It has features that distinguish it from the described amplifier. Among the important features is that the relative flat gain spectrum has a low reversal rate (0.6-0.7 vs. 0.4), and the erbium-doped fiber length is equivalent to about 75m, up to about 300m While longer or longer lengths are required, typical C-band devices are equal to or less than about 50 m. This is because the relative emission cross section of erbium is small at least for wavelengths longer than around 1560 nm. The significance of the very long erbium-doped fiber length required for low-inversion amplification is that large-scale backward-propagating amplified spontaneous emission (ASE)
) In the generation of light. Further, the characteristics of the environment using the L band strongly influence the selection of the excitation wavelength for the 980 nm absorption band. In any case, erbium-doped fiber (EDFA) L-band amplifiers have become a fundamental enabling technology for systems that operate within what is referred to as a fourth generation communication window.

[0004] The use of a pump wavelength that is primarily intended to relieve the wavelength constraints of a semiconductor pump laser diode of 980 nm, and a detuned pump wavelength in the 980 nm band for C-band amplification, is numerous. Reported by the author. Pederson
on) et al. measured small signal gain and noise properties of erbium-doped fiber intensity amplifiers pumped in the 980 nm band as a function of fiber length and pump wavelength.
This is described in IEEE Photonics Technology Letters, Volume 4, Volume 4, 351-35.
Page 3 (April 1992), "Gain and Noise Loss for Excitation of Erbium-Doped Fiber Intensity Amplifier by Detuned 980 nm Pump Light" (Gain and Noise Penalty)
for Detuned 980nm Pumping of Erbium-Doped Fiber Power Amplifiers, IEEE
Photonics Technology Letters, Vol. 4, No. 4, pp. 351-353 (April 1992)). The report showed that the output signal for a C-band input signal at 1551 nm decreased as the excitation light wavelength was detuned by ± 20 nm from the 979 nm absorption peak. Pederson et al. Examined the effect of detuning the excitation wavelength on multiple small-signal erbium-doped fiber amplifiers (EDFAs) for C-band input signals at 1532 nm and 1551 nm. This is described in "Gain and Noise Characteristics of Small-Signal Erbium-Doped Fiber Amplifiers Pumped in the 980 nm Band" (Gain, IEEE Photonics Technology Letters, Vol. 4, pp. 556-558, June 1992). and Noise Properties of Small-Signal Erbium-Doped Fi
ber Amplifiers Pumped in the 980-nm Band, IEEE Photonics Technology Let
ters, Vol. 4, No. 6, pp. 556-558 (June 1992)), particularly in FIG.
Percival et al., Provided that the fiber had the correct cut-off wavelength, had an excitation range extension of 38 nm with a center wavelength of 980 nm.
A constant gain for C-band input signal at 6nm was reported. This is described in “Electronic Letters Vol. 27, Vol. 14, pp. 1266-1268 (July 1991)“ 966-10
Erbium-doped fiber amplifier with constant gain by 04nm pump wavelength ”(Erbi
um-Doped Fiber Amplifier With Constant Gain For Pump Wavelengths Between
966 to 1004nm, Electronics Letters, Vol.27, No.14, pp.1266-1268 (July 19
91)).

[0005] Unlike these reports, the present invention provides a method for large signal input strength L-band amplification.
This is related to the unevaluated advantage of 0 nm excitation detuning light. These benefits include L-band gain and improved pump signal conversion efficiency. Here, the large signal input strength is related to the input signal state for an optical amplifier that is in saturation and producing an output signal strength that is essentially independent of the input signal strength. . That is, the output signal strength depends on the excitation strength, and has a relationship of P _out = KP _pump . Here, K represents the amplification efficiency. On the other hand, the output signal strength and supplies the small signal amplification by the gain of the amplifier or amplifier, depending on the input signal strength, P _out
= GP _in . These are well known to those skilled in the art.

[0006]

[Problems to be solved by the invention]

The present invention relates to a method and apparatus, including improving L-band optical signal amplification by pumping with a detuned 980 nm band to improve gain and pump-to-signal light conversion efficiency. . Further features and advantages of the invention will be set forth in the following description, and will be apparent from the practice of the invention. The objects and other advantages of the invention will be realized and attained by the particularly particularly pointed out description and appended claims, as well as the devices and methods illustrated in the drawings.

[0007]

[Means for Solving the Problems]

Embodiments of the present invention are directed to the long wavelength spectral region, i.e., the region from about 1560 to about 1615 nm,
The present invention relates to a method of driving an optical amplifier for amplifying an optical signal in the optical amplifier. This spectral region is
It is also referred to below and is known to those skilled in the art as the L-band of the rare earth doped gain medium. It is known that a rare-earth-doped gain medium has an excitation absorption band centered at about 980 nm and an absorption band centered at about 1480 nm, the former being very important in the present invention. This embodiment includes inputting an optical signal having a large signal intensity to the amplifier and pumping the gain medium with pump light having a wavelength different from the known center wavelength of the pump absorption band. In various aspects of this embodiment, the center wavelength of the known pump absorption band is about 980 nm, and the gain medium is a waveguide of a rare earth-doped optical fiber, preferably an erbium-doped fiber, wherein the pump light wavelength is The gain medium is between 0 and 30 nm above and below the wavelength, preferably between 5 and 30 nm above and below the center wavelength, and generally the gain medium between 100 and 300 m has a length equal to or greater than about 75 m .

Another embodiment of the present invention is directed to a method of driving an optical amplifier that amplifies an optical signal in the L band of a rare earth doped gain fiber emission spectrum having a known pump absorption band.
The method includes the steps of inputting an optical signal having a large signal input intensity to the amplifier, and providing the amplifier with pump light detuned from the center wavelength of a known pump absorption band corresponding to the optical signal signal to be pumped. include. Here, the detuned pump light acts to supply an amplified output signal having a stronger intensity than the output signal strength obtained from the pump center wavelength. In various aspects of this embodiment, the known excitation absorption band is about
980 nm, the gain medium is a waveguide of a rare earth-doped optical fiber, preferably an erbium-doped fiber, and the excitation light wavelength is 0 to 30 n above and below the center wavelength.
m, and preferably in the range 5-30 nm above and below the center wavelength, and generally between 100-300 m, the gain medium has a length equal to or greater than about 75 m.

Another embodiment relates to a method of driving an optical amplifier that amplifies an optical signal in the L band of a rare earth doped gain fiber emission spectrum having a known pump absorption band.
The method includes the steps of inputting an optical signal having a large signal input strength to an amplifier and pumping a gain medium with pump light having a wavelength detuned from a known center wavelength of a pump absorption band. . Here, the amplified spontaneous emission light (ASE) traveling in the direction opposite to the direction of the excitation light is measured to be less than the opposite traveling amplified spontaneous emission light (ASE) measured at the excitation band center wavelength.

A further embodiment is a rare earth having a known excitation absorption wavelength corresponding to an input optical signal having an emission spectrum and desired to be amplified in the L band region of the emission spectrum, here an optical signal having a large input signal intensity. The present invention relates to an amplifier comprising a doped gain stage and a pump light source using a wavelength different from the center wavelength of the pump absorption band, and connected to the gain stage. The amplified signal output from the amplifier is substantially stronger in the output signal strength due to the detuned excitation wavelength than the output signal due to the excitation at the excitation center wavelength. In various aspects of this embodiment, the excitation center wavelength is about 980 n
m, the detuned excitation wavelength is in the range of 0-30 nm above and below this center wavelength,
It is preferably in the range of 5 to 30 nm above and below the excitation center wavelength.

[0011] The foregoing summary description and the following detailed description are exemplary, and provide a further description of the claimed invention. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which provide further understanding of the invention, illustrate embodiments of the invention and are a part of this specification and illustrate the principles of the invention.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an experimental apparatus for measuring the optical signal output intensity, backward amplified spontaneous emission (ASE), excitation intensity, and residual excitation intensity. By using the device schematically shown in FIG. 1, the effect of changing the excitation wavelength having an absorption peak at about 980 nm is affected by the large input intensity and the optical signal in the erbium L band. And experimented in detail. A tunable Ti sapphire pump laser 12 (not shown, but pumped by an Ar ion laser) provides 3 dB
Connected to pigtail 32 of coupler 16. Half of the input pump light was directed from the 3 dB coupler 16 to an intensity detector 18 indicated by the double diamond in FIG. The residual pump light was guided from a wavelength multiplexer (WDM) 20 to an active amplification fiber 26 consisting of 100 m of type I erbium fiber. DFB laser 22, used as an optical signal source, 1565nm
Was output. This saturated signal passed through an isolator 24 and a tap coupler 28, and was supplied to an active fiber 26 by a wavelength multiplexer (WDM) 20. A wavelength multiplexer (WDM) 36 downstream of the active fiber 26 propagates the amplified optical signal through an isolator 38, passes through an optical bandpass filter 40, and measures an optical signal output intensity (not shown). ) Sent to. On the other hand, the residual excitation intensity was supplied from a wavelength multiplexer (WDM) 36 to an intensity monitor 42 indicated by a double diamond mark. The optical bandpass filter is centered at 1565nm (signal wavelength) and 1nm-3
Has a dB bandwidth.

As is well known to those skilled in the art, amplified spontaneous emission (ASE) is generated in the active fiber 26 due to excitation by the excitation light, and a portion of this amplified spontaneous emission (ASE) It travels in the opposite direction, that is, in the direction against the input optical signal. This backward amplified spontaneous emission light (ASE) travels from the wavelength multiplexer (WDM) 20 through the waveguide 34 to the tap coupler 28, and after passing through the coupler 28, 5% of the backward amplified amplified spontaneous emission light (ASE) ) Was entered into the intensity monitor 30 by a double diamond mark. In an exemplary embodiment of the invention, the DFB
The optical signal output from the laser 22 was adjusted to 1565 nm. Under this signal wavelength, four sets of measurement data indicate the input signal strength as a) 2.0 dBm, b) 0.15 dBm, c) -4.93 dBm, d) -9.
Obtained by changing to 91 dBm. Note that any of the setting conditions is sufficient for saturation of the erbium-doped fiber 26. Output power is measured at the output of the optical fiber and includes passive losses due to wavelength division multiplexers (WDM) (0.5 dB), isolators (0.6 dB), and optical bandpass filters (1.4 dB).

The pump laser 12 provided a tunable output signal with a constant intensity of 20 dBm (+/− 0.3 dB). In case C), the input intensity per channel is approximately equivalent to 32 channels of -20 dBm, and as a result of tuning the excitation wavelength from 980 nm to 954 nm (-26 nm) or 1007 nm (+27 nm), the output signal intensity becomes A 3dB increase was seen. Such an increase in the efficiency of pumping light-signal light conversion is shown in FIG. FIG. 2 shows (a) and (b) described above.
), And (d) also show the relationship between the signal intensity and the excitation wavelength for each case, and the minimum gain values of the input signal intensity for the four cases a to d are 13 dB, 14.6 dB, 1
It corresponds to 7.2 dB and 19.4 dB. The increase in signal intensity as a function of the excitation wavelength detuned from the center wavelength of the 980 nm excitation absorption band is attributed, at least in part, to a decrease in retrograde amplified spontaneous emission (ASE). Figure 3 shows the retrograde amplified spontaneous emission light (ASE
) Shows the measured values. The backward amplified spontaneous emission (ASE) also depends on the coil length.
As described above, the erbium-doped fiber 26 has a length of 100 m, and all optical input signal intensities are large input signals as described above. The effect on detuned pump light wavelength and output signal strength shown in FIG. 2 is due to previously reported research results for C-band amplifiers used in self-saturating situations (ie, situations using small signal input strength). Is the same as However, there is no practical interest in this result. Excitation light absorption in erbium fibers also appears and plays a role in the described phenomenon. We hypothesize that retrograde amplified spontaneous emission (ASE) intensity and excitation absorption are independent. Although not measured, we expect that the noise value will increase as the pump wavelength detunes from the absorption peak due to a decrease in the front end reversal of the gain medium.

According to the above-described exemplary embodiment, in the range of 0 to 30 nm above and below the center wavelength of the excitation absorption band, the excitation wavelength detuned by +27 or -26 nm is used in an environment using L-band signal amplification. In, it has provided improved gain and conversion efficiency. In particular, at 1565 nm, -4
For an input signal strength of .93 dBm, a 3 dB improvement was obtained with a wavelength detuned from the 980 nm excitation center wavelength. In addition to the advantages described above, it may be possible to change from a 1480nm pump light with technical issues (eg heat loss) or sales issues (eg availability or price) to a detuned 980nm pump laser diode in an L-band amplifier. obtain.

According to another embodiment of the invention illustrated in FIG. 4, optical amplifier 80 includes a rare earth-doped fiber gain stage 82, preferably of erbium-doped fiber. The rare earth-doped fiber gain stage has the L-band emission spectrum shown in FIG. 5, and the rare earth-doped fiber gain stage has approximately a corresponding gain to amplify the input signal.
It has a known excitation wavelength absorption band centered at 980 nm. The input signal has a large input signal strength that can saturate the gain medium, and its wavelength is in the emission spectral region, which is a long wavelength region, preferably in the L band region extending from about 1560 to 1615 nm. An excitation light source 84 that supplies light to the 980 nm excitation band operates at a wavelength detuned from the center wavelength of 980 nm, preferably in the range of +/- 5 to 30 nm from the center wavelength. As shown, the excitation light is introduced into the erbium-doped fiber through the coupler 86. Other excitation methods are possible. For example, in the detuning excitation region,
In the case of using the pumping light intensity of the forward traveling (that is, propagating with the signal), using the pumping light reflector, the remaining pumping light is re-injected into the fiber in the counter-propagating direction, and the input of the active fiber is used. It is also possible to reverse the direction. This is a method known to those skilled in the art. Pump light in the same or opposite direction is also considered. The pump light in the opposite direction alone does not seem to be beneficial for the good noise characteristics of the amplifier due to the need to keep the front end inversion high.

The above-described exemplary embodiments of the method of the present invention are fully applicable to the amplifier embodiments described herein. It will be apparent to those skilled in the art that various modifications and variations can be made in the apparatus and method of the present invention without departing from the spirit and scope of the invention. It is therefore intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims or their equivalents.

[Brief description of the drawings]

FIG. 1 is a general view showing an embodiment of an experimental apparatus according to the present invention for measuring excitation intensity, output signal intensity, backward amplified spontaneous emission, and residual excitation intensity.

FIG. 2 is a graph showing output signal strength as a function of pump wavelength for four input signal strengths of the present invention.

FIG. 3 is a graph illustrating a retro-amplified spontaneous emission intensity with respect to an excitation wavelength for four input signal intensities according to an embodiment of the present invention.

FIG. 4 is an overall view of an embodiment of the amplifier of the present invention.

FIG. 5 is a graph showing typical emission characteristics of a type I erbium fiber.

[Explanation of symbols]

 18 Intensity detector 26 Rare earth doped fiber 30 Intensity detector 42 Intensity monitor 82 Rare earth doped fiber 84 Excitation light source 86 Coupler

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Claims (19)

[Claims] 1. A method for driving an optical amplifier for improving gain and pump light-signal light conversion efficiency in a long wavelength region (L band) of a rare earth doped gain medium emission spectrum having a known pump absorption band, (a) providing an optical signal having a large signal input intensity to the amplifier; (b) providing the amplifier with pump light having a pump light wavelength different from the center wavelength of the known pump absorption band; A method for driving an optical amplifier, comprising: amplifying a signal. 2. The method according to claim 1, wherein said excitation light wavelength is in a range of about ± 30 nm from a center wavelength of a known excitation absorption band. 3. The excitation light wavelength is about ± 5 to 30 n from the center wavelength of a known excitation absorption band.
3. The method according to claim 2, wherein the distance is in the range m. 4. The method of claim 1, wherein said amplifier comprises a rare earth doped fiber gain medium. 5. The method of claim 4, wherein said rare earth doped fiber includes erbium as an excitation light absorbing dopant. 6. The method of claim 4, wherein the rare earth doped fiber of the amplifier has a length equal to or greater than about 75 m. 7. The method of claim 2, wherein the center wavelength of the known excitation absorption band is about 980 nm. 8. The method of claim 3, wherein the center wavelength of the known excitation absorption band is about 980 nm. 9. The method of claim 1, wherein said L band is a band from about 1565 to about 1615 nm. 10. A method for driving an optical amplifier for improving gain and pump light-signal light conversion efficiency in a long wavelength region (L band) of an emission spectrum of a rare earth doped gain medium having a known pump absorption band. (A) providing an optical signal having a large signal input intensity to an amplifier; and (b) providing an optical signal having a wavelength detuned from the center wavelength of a known excitation absorption band to the amplifier. And amplifying the amplified signal intensity value at the detuned pump wavelength as compared with the amplified signal intensity at the center wavelength of the pump band. 11. The method according to claim 1, wherein the step of applying the pumping light to the amplifier detunes the pumping light wavelength from a center wavelength in a range of about ± 5 to 30 nm.
0. The method of claim 0. 12. The method of claim 10, wherein the center wavelength is about 980 nm.
The described method. 13. The method according to claim 10, wherein said L band is a band of about 1565 to about 1615 nm. 14. A method for driving an optical amplifier, which improves gain and pump light-signal light conversion efficiency in a long wavelength region (L band) of an emission spectrum of a rare earth doped gain medium having a known pump absorption band. (A) providing an amplifier with an optical signal having a large signal input intensity; and (b) providing the amplifier with a pump light having a wavelength detuned from the center wavelength of the known pump absorption band. The measured value of the amplified spontaneous emission light (ASE) traveling in the opposite direction to the excitation light is larger than the measured value of the amplified spontaneous emission light (ASE) at the center wavelength of the excitation band. A method of driving an optical amplifier. 15. The method of claim 14, wherein the step of providing the pumping light to the amplifier detunes the pumping light wavelength in a range from about ± 5 to 30 nm from the center wavelength. 16. The center wavelength is about 980 nm.
The described method. 17. The method of claim 14, wherein the L band is a band between about 1565 and about 1615 nm. 18. A rare earth-doped gain stage having an emission spectrum and a known excitation wavelength absorption band and amplifying a signal having a wavelength in the long wavelength region of the emission spectrum and an input signal having a large input signal. An excitation light source connected to the gain stage and emitting a drive wavelength different from the center wavelength of the pump absorption band, wherein the amplified output signal intensity is such that the drive wavelength is substantially equal to the center wavelength. An optical amplifier having a stronger intensity at a detuned drive wavelength than an output signal at almost the same wavelength. 19. The long wavelength region of the emission spectrum is a band of about 1565 to about 1615 nm, the center wavelength is about 980 nm, and the driving wavelength is about ± 5 to 30 nm from the center wavelength. 19. The amplifier according to claim 18, wherein: